This application relates generally to gas turbine engines and, more particularly, to gas turbine engines including exhaust centerbodies.
Gas turbine engines often include exhaust augmentors to increase overall engine performance and a centerbody is used to lower the velocity of the air and gas flows entering the augmentor. The centerbody is typically positioned coaxial with a center longitudinal axis of the gas turbine engine and extends from a turbine core at least partially into the augmentor. Because of engine weight considerations, such centerbodies are fabricated from thin sheet metal. Such thin centerbody shells have relatively low natural frequencies and may be subject to potentially damaging resonance or vibrations generated during engine operation.
In an effort to prevent such potentially damaging vibrations from having an adverse effect on the centerbody, stiffeners are used to structurally support the centerbody. The stiffeners are attached to an inner surface of the centerbody shell and extend radially inward. A cavity is defined between the stiffener and the centerbody shell. During operation, cooling air is channeled within the centerbody and around the stiffener to prevent the centerbody from overheating. As the gas turbine engine is accelerated from an idle operating condition to an increased power condition, the outer surface of the centerbody is exposed to high temperature gas flows. As a result of heat transfer and the cooling air, an outer surface of the centerbody is exposed to much higher temperatures than the stiffener. Upon deceleration of the engine, the opposite effect occurs between the centerbody surface and the stiffener. As a result of the temperature differences, thermal stresses develop between the stiffeners and the centerbody shell. Such thermal stresses often lead to a failure of the centerbody.
In an exemplary embodiment, a centerbody for a gas turbine engine includes a thermal control system which minimizes thermal stresses between a centerbody and at least one centerbody stiffener. The centerbody includes a at least one stiffener attached to a centerbody shell and extending radially inward. Each stiffener and the centerbody shell define a cavity. The thermal control system includes a plurality of openings extending through the centerbody shell into each cavity. The openings are located circumferentially disposed around the centerbody and include pairs of corresponding entrance openings and exit openings. Each entrance opening is disposed circumferentially from each exit opening.
In the exemplary embodiment, each entrance opening is positioned downstream from each frame strut of the engine. Each exit opening is positioned between two circumferentially adjacent frame struts.
During operation, because the entrance openings are positioned downstream from the frame struts, the entrance openings are exposed to wake airflow. In contrast, the exit openings are directly in the flowpath of the airflow. As a result, a pressure differential develops between the entrance openings and the exit openings. Such a pressure differential permits circumferential flow to develop within the cavity. As a result, less thermal differences exist between each stiffener and the centerbody. Additionally, the temperature of each stiffener increases and decreases more rapidly as engine operating power levels are changed. Furthermore, circumferential temperature variations within the centerbody are minimized. As a result, less thermal stresses are induced within the centerbody.